Ultraviolet (UV) radiation has been implicated as a major environmental contributor to the development of most cutaneous melanomas. Sunscreens and sun awareness behavior have been used for the prevention of cutaneous melanoma, but their clinical utility remains mixed. The mechanistic role of UV radiation in melanomagenesis needs to be more comprehensively defined. However, it is known that in human skin, UV radiation not only generates reactive oxygen species (ROS), but also produces a marked increase of nitric oxide (NO). (Russo P. A., Halliday G. M. Inhibition of nitric oxide and reactive oxygen species production improves the ability of a sunscreen to protect from sunburn, immunosuppression and photocarcinogenesis. Br. J. Dermatol. 2006; 155:408-15). While the contributions of ROS to melanomagenesis have been extensively studied, characterizations of effects of NO stress and its detailed molecular mechanisms have been limited.
NO, produced from L-arginine by nitric oxide synthase (NOS), leads to highly reactive oxidants such as peroxynitrite, resulting in DNA damage even in physiologically relevant ranges of NO. In the skin, NO-mediated signaling also contributes to UV-induced melanogenesis and pigmentation. (Romero-Graillet C., Aberdam E., Clement M., Ortonne J. P., Ballotti R. Nitric oxide produced by ultraviolet-irradiated keratinocytes stimulates melanogenesis. J. Clin. Invest. 1997; 99:635-42.) Large quantities of NO have been detected in many types of cancer tissues, and the role of NO in carcinogenesis, tumor growth and metastasis has been well documented in skin cancer and other tumors. Constitutive production of NO in melanoma resulted in increased proliferation, impaired immune response, and lymphangiogenesis, associated with poor survival in patients. (Grimm E. A., Ellerhorst J., Tang C. H., Ekmekcioglu S. Constitutive intracellular production of iNOS and NO in human melanoma: possible role in regulation of growth and resistance to apoptosis. Nitric Oxide. 2008; 19:133-7; Massi D., De Nisi M. C., Franchi A., Mourmouras V., Baroni G., Panelos J., et al. Inducible nitric oxide synthase expression in melanoma: implications in lymphangiogenesis. Mod. Pathol. 2009; 22:21-30; Ekmekcioglu S., Ellerhorst J. A., Prieto V. G., Johnson M. M., Broemeling L. D., Grimm E. A. Tumor iNOS predicts poor survival for stage III melanoma patients. Int. J. Cancer. 2006; 119:861-6.)
The NOS family comprises inducible NOS (iNOS), endothelial NOS (eNOS), and neuronal NOS (nNOS), the latter of which is expressed mainly in neural tissue. Previous studies have largely focused on iNOS and its inhibitors, which exhibited promising chemopreventive activities in skin carcinogenesis but limited anti-melanoma potential. As melanocytes originate from the neural crest and have many gene expression characteristics similar to neural cells, nNOS may play a unique role in regulating NO levels in melanocytes. In contrast to iNOS-mediated generation of high levels of NO, nNOS produces lower levels of NO and mediates direct cellular effects such as neuromodulation. In a 1999 study, a progressive increase of nNOS expression was evident over the course of melanoma progression, suggesting that the de novo expression of nNOS may be a marker for an early stage of melanoma. (Ahmed B., Van Den Oord J. J. Expression of the neuronal isoform of nitric oxide synthase (nNOS) and its inhibitor, protein inhibitor of nNOS, in pigment cell lesions of the skin. Br. J. Dermatol. 1999; 141:12-9.) Differential expression of nNOS in tumorigenic and non-tumorigenic variants derived from the same melanoma cell line also has been reported. A recent clinical epidemiologic study investigated the role of polymorphisms of nNOS as related to outcome and demonstrated that certain nNOS (but not iNOS) genotypes were associated with an increased risk of cutaneous melanoma. (Li C., Hu Z., Liu Z., Wang L. E., Gershenwald J. E., Lee J. E., et al. Polymorphisms of the neuronal and inducible nitric oxide synthase genes and the risk of cutaneous melanoma: a case-control study. Cancer. 2007; 109:1570-8.) Moreover, this study also identified significant interactions of the combined nNOS genotypes and moles and the lifetime number of blistering sunburns.
With increasing evidence of the role of nNOS in melanoma progression, the art is likewise concerned with and directed to a search for specific nNOS inhibitors and related methods of melanoma treatment and prevention.